Precise control over post-cardioplegia reperfusion, including an initial period of asystolic reperfusion, has been proposed as a means to minimize post-cardioplegia reperfusion injury. This methodology is based upon studies of the biochemical, rheologic, and histologic aspects of controlled post-cardioplegia reperfusion. The present study will examine electrophysiologic aspects of post-cardioplegia reperfusion. The primary hypothesis is that reperfusion ventricular fibrillation results from transient regional electrophysiologic heterogeneity due to incomplete electrophysiologic recovery of the heart and can be minimized by appropriate modifications of reperfusion. Electrophysiologic data will include recordings of atrial and ventricular electrograms as well as recordings of the specialized conduction system (AV node/His bundle and right bundle branch). During reperfusion the changes in several biochemical variables (myocardial high energy phosphate levels and coronary sinus pH, PO2, PCO2, and lactate) will be measured for subsequent correlation with the electrophysiologic events. Six separate experiments were designed to examine the electrophysiology of controlled post-cardioplegia reperfusion in normal hearts and in hearts with regional ischemia or left ventricular distension. These experiments will investigate the effects of different durations of asystolic reperfusion and different aortic perfusion pressures on the incidence of reperfusion ventricular fibrillation. The sixth experiment will examine regional blood flow during reperfusion asystole and reperfusion ventricular fibrillation in normal hearts and in hearts with regional ischemia or left ventricular distension. The sixth experiment will test the hypothesis that ventricular fibrillation results in reperfusion maldistribution that is especially severe in a distended ventricle or in a collateral dependent region of myocardium. The proposed study will improve our understanding of the electrophysiologic events that occur during post-cardioplegia reperfusion and evaluate two methods to modulate the incidence of reperfusion ventricular fibrillation. This information may suggest better methods to provide a period of asystolic reperfusion followed by the prompt resumption of a sinus rhythm. The long range goal of subsequent studies will be to define relationship between the electrophysiologic, biochemical, and functional recovery of the post-ischemic reperfused heart.